This invention pertains to bosses which are slotted and are secured to spindles by a pinch bolt which draws the ends of the bosses onto the spindle. Such spindles may be serrated, splined, keyed, or cylindrical. It particularly pertains to serrated bicycle crankshaft spindles which mount internally-serrated crank arm bosses, which are slotted and have a pinch bolt which secures them to the spindle. It also pertains to slotted stem bosses which are secured to cylindrical bicycle steering tubes by a pinch bolt.
Where bicycle crank arms are secured to serrated spindles by a pinch bolt, the arm is apt to work its way off the spindle, even though it is tightly clamped by the pinch bolt, in an installation showing no looseness between the arm and the spindle. Without some means of locking the arm to the spindle, a crank arm can move 1/2" off a spindle in as little as 10 minutes of cycling.
In some bicycles, the handlebars are secured to a handlebar stem, and the handlebar stem is secured to a slotted stem boss, which is in turn secured to a cylindrical steering tube by a pinch bolt.
Where such a slotted stem boss is secured to a cylindrical steering tube of a bicycle, some means for positively preventing the boss from coming off. Also, a device is needed to keep such a stem boss from an excessive amount of turning, in the event of a loose or broken pinch bolt; some turning is acceptable, since it would not cause loss of control.
Several devices have been used to prevent bosses of both types from coming off, such as snap rings, end bolts and washers, or by machining a groove in the spindle to partially engage the pinch bolt, such that the boss can't be removed from the spindle without first withdrawing the pinchbolt from the arm.
Each of these devices has at least one disadvantage:
Snap rings require an additional length of spindle, protruding beyond the end of the boss, which may interfere with the cyclist's ankle, and which require extra machining, and require snap ring installation tools to mount or remove the snap rings.
Machining a groove in the spindle weakens the spindle, particularly if the pinch bolt is positioned in the middle of the boss, as it usually is. Such grooves must either be turned in a lathe or milled.
End bolts and washers add extra weight and require extra machining. They also protrude and may interfere with a cyclist's ankle.